1. Field of the Invention
The present invention relates to a retaining structure for a platen roller used while in contact with a recording head, and a recording apparatus having the retaining structure.
2. Description of the Related Art
Conventionally, there are available recording apparatuses having inside a casing a recording head and a platen roller held in contact therewith, with the recording head performing recording on a recording medium conveyed by the platen roller. In such a recording apparatus, when performing operations, such as the setting of the recording medium, jamming treatment, and maintenance and replacement of the recording head and the platen roller, the operations are very hard to perform when the recording head and the platen roller remain in contact with each other. Accordingly, it is desirable to separate the platen roller and the recording head from each other and expose them to the exterior of the casing. It is desirable for the recording head, which has a plurality of recording elements (e.g., heat generating elements), to be fixed in position inside the casing so as not to impair the reliability of the electrical connection for inputting recording signals for selectively driving the recording elements. In view of this, a construction is generally adopted in which the platen roller is separated from the recording head and extracted to the exterior, with the recording head remaining secured in position inside the casing.
During recording operation, it is necessary for the platen roller to be firmly held in contact with the recording head with a predetermined pressure. Thus, in some constructions, a groove-like recess is provided in the casing, and the platen roller is retained in the recess to thereby effect positioning.
Further, to make the platen roller detachable, a construction is available in which there is provided a spring member, for example, at the opening portion of the recess, that is, at the portion through which the platen roller is let in and out. In this construction, it is possible to elastically deform the spring member and push in the platen roller to a predetermined position in the recess. However, once forcibly brought to the predetermined position, the platen roller cannot be extracted from the recess unless the spring member undergoes elastic deformation again to open the opening portion. When the user applies a force to the spring member to elastically deform the same, the platen roller can be easily removed.
Apart from this, there is a construction in which the shaft portion of the platen roller is retained in the recess by means of a member surrounding the same. That is, at least a part of the opening portion of the recess (entrance portion for platen roller) is blocked to thereby prevent the platen roller from getting out of the recess. The member blocking the opening portion of the recess may be the recording head itself, or a dedicated lock arm for retaining the shaft portion of the platen roller (JP 2000-318260 A). In such a construction, by moving the member surrounding the shaft portion of the platen roller (recording head or lock arm), the opening portion of the recess is opened, and attachment/detachment of the platen roller becomes possible.
JP 2000-118060 A discloses a construction in which a cover plate (cover member) that can be opened and closed with respect to a main body frame (casing base member) is equipped with a first slit into which the shaft portion of the platen roller is inserted, with the main body frame being equipped with a second slit that is to be combined with the first slit to thereby retain the shaft portion of the platen roller when the cover plate is closed. Further, in this construction, a lock lever rotatably provided on the cover plate is engaged with a pin provided on the main body frame, thereby making it possible to fix the cover frame to the main body frame in a state in which the platen roller is retained at the position where the first slit and the second slit join each other.
JP 06-71954 A discloses a construction in which the platen roller has a rotatably mounted bush lever member, and in which a substantially rectangular shaft portion is formed on the bush lever member, with the casing being provided with a recess whose opening portion has a width allowing passage of the shorter side of the rectangular shaft portion but not allowing passage of the longer side thereof. In this construction, the shaft portion of the bush lever member is inserted into the recess, with the shorter side of the substantially rectangular shaft portion being opposed to the opening portion of the recess, and then the bush lever member is rotated by 90 degrees to cause the longer side of the substantially rectangular shaft portion to be opposed to the opening portion of the recess, thereby preventing the shaft portion and the platen roller from getting out of the recess.
Of the above-described conventional examples, the construction in which a spring member is provided at the opening portion of the recess into which the platen roller is inserted, requires provision of an appropriate spring force corresponding to the position and configuration of the spring member. If the spring member does not easily undergo elastic deformation, it is difficult to open the opening portion of the recess, so that the operation of the attachment/detachment of the platen roller is not easy to perform. On the other hand, when the spring member easily undergoes elastic deformation, the spring member may be easily allowed to be elastically deformed by some impact, vibration, etc. even when the user applies no external force thereto, with the result that the platen roller is inadvertently allowed to get out of the recess. It is not easy to accurately realize an appropriate spring force which prevents the platen roller from getting out of the recess during normal recording and which easily allows elastic deformation of the spring member when the user performs attachment/detachment operation. Further, the spring force may change as a result of long-term use, which may lead to a problem regarding the attachment/detachment of the platen roller.
In the construction in which the recording head itself is provided at a position where it blocks the opening portion of the recess to prevent the platen roller from getting out of the recess, there is provided a spring member for pressing the recording head against the platen roller to realize satisfactory recording. As in the above-described construction, this spring member regulates the attachment/detachment of the platen roller. Thus, when the spring member mounted to the recording head is stiff, it is difficult to open the opening portion of the recess, and the operation of attaching/detaching the platen roller is not easy to perform. On the other hand, when the spring member is flexible, the recording head may inadvertently retreat due to some impact, vibration, etc. even when the user applies no external force, with the result that the platen roller is allowed to get out of the recess. It is by no means easy to accurately realize an appropriate spring force which prevents the platen roller from getting out of the recess during normal recording, which can cause the recording head to abut the platen roller with an appropriate pressure, and which, when the user performs attachment/detachment operation, easily allows the spring member to undergo elastic deformation so that the platen roller can be inserted into the recess. Further, the spring force may change as a result of long-term use, which may lead to a problem.
In the construction in which, as disclosed in JP 2000-318260 A, the opening portion of the recess is blocked by a lock arm, the lock arm is usually provided on the base member side of the casing, and is can be moved by an operating lever or the like. That is, the fulcrum for the movement of the lock arm is generally situated in the vicinity of the recording head or at the rear of the recording head. Further, to retain the lock arm at the position where it blocks the opening portion of the recess, there is often provided a spring member to urge the lock arm. Due to the provision of the operating lever, the operability in attachment/detachment ceases to depend solely upon the spring force of the spring member as in the constructions described above. In this construction, however, a fulcrum for the operation of the lock arm, the operating lever, the spring member, etc. are usually arranged on the base member of the casing, in particular, in the vicinity or at the rear of the recording head. As a result, the space in the central portion of the casing is occupied by those members, so it is necessary to separately provide a space for arranging other members related to the various functions of the recording apparatus, and the conveyance route for the recording medium is restricted due to the above-mentioned members, which reduces the degree of freedom in terms of design, and constitutes a hindrance to a reduction in the size of the apparatus as a whole.
The construction as disclosed in JP 2000-118060 A, in which the operating lever is provided not on the main body frame but on the cover frame, is more advantageous than the construction as disclosed in JP 2000-318260 A in that it is possible to effectively utilize the space on the main body frame (casing base member) side. However, this construction, in which the platen is separated from the recording head by moving the entire cover frame, involves a large operational stroke, resulting in a large operating lever. This leads to a reduction in the degree of freedom in terms of installation space for the apparatus. Further, in this construction, in which the platen roller is retained in the first slit, the opening portion (entrance portion) of the first slit is narrowed.
In the construction as disclosed in JP 06-71954 A, the bush lever member, which is relatively large, is rotated by 90 degrees, so a large stroke is involved, and it is necessary to provide a moving space for the bush lever member. Further, the bush lever member is fixed in position, with the platen roller inserted in the recess, so it is necessary to provide a lock portion for the bush lever member and a structure for locking the opening of the casing. Further, it is necessary to strictly maintain the following relationship: the length of the longer side of the substantially rectangular shaft portion> the width of the opening portion of the recess> the length of the shorter side of the shaft portion. If the difference between those dimensions is slight, the reliability in locking deteriorates, so a reduction in size to an extreme degree is impossible.